Ignore serde attributes specta does not model (fixes remote = "Self")

[agasparovic]

When the serde feature is enabled, parse_container_meta / parse_variant_meta / parse_field_meta return Ok(()) for serde attribute keys they do not recognize without consuming the attribute's value. syn's parse_nested_meta then hits the unconsumed = value tokens and fails the whole derive with expected ,``, so the type silently loses its Type impl and downstream crates fail with "the trait `specta::Type` is not implemented".

Any legal serde name-value or list attribute outside the subset specta models triggers this: container remote / bound / expecting, variant bound, field getter. The one that bit us is #[serde(remote = "Self")] on FlightData in the fltsci repo - the pattern that makes serde emit its derived serialize/deserialize functions as inherent items so the trait impls can be hand-written (migrate-then-parse for the durable JSON schema versioning design). Building flights_api alone worked, because nothing there enables specta-macros/serde; any build including specta-serde (DX bindings, payload-compatibility checker, rust-analyzer workspace checks) failed.

Fix: an else branch in each of the three parsers that consumes and discards the value (= <expr> or a parenthesized list). serde validates its own attribute namespace - a typo still fails the serde derive itself - so specta's job is only to skip what it does not model, including attributes serde adds in the future.

Tests: tests/tests/serde_unknown_attrs.rs covers all five attributes above and asserts the exported shape is unaffected. Before the fix, that file fails to compile with five expected ,`` errors. Also verified end-to-end with a scratch crate mirroring the fltsci setup (serde_with::apply + `Type` derive + `remote = "Self"` + hand-written trait impls delegating to the inherent functions, with `specta-serde` in the graph): round-trip works and `PhasesFormat` exports the correct phase-specific shapes.